1. Field of the Invention
The present invention relates to a device for matching an antenna impedance in a portable radio telephone, and more particularly, to a device for matching an antenna impedance in a portable radio telephone, for maintaining an optimal antenna impedance matching state.
2. Background of the Related Art
The portable radio telephone of a folder type, or a type similar to the folder type, is provided with an upper casing and a lower casing for protecting a display and a keypad. Since an antenna related impedance is varied with the state of the casing, (i.e., a folded or closed state and an unfolded or open state), the radio performance characteristics also vary. That is, the radio performance of the portable radio telephone is dependent on the state of the casing. An example of such a portable radio telephone is disclosed in U.S. Pat. No. 5,335,368, wherein a portable radio telephone having a casing is disclosed which maintains a matched state for the antenna impedance in a call waiting state and in an operating state. The portable radio telephone is provided with an upper casing and a lower casing foldably coupled to a body by hinges, a matching circuit between the antenna and a transmitting-and-receiving circuit, and a sensor (a switch) for sensing states (folded or unfolded) of the upper casing and the lower casing for changing an impedance matching state according to a power provided to the sensor.
However, the foregoing device for matching an antenna impedance has the following problem.
First, in the related art, sensors switched mechanically are used for sensing folding and unfolding of the upper casing and the lower casing and matching an impedance of the antenna. Therefore, the sensor is sensitive to mechanical defects, and no antenna related impedance matching dependent on the casing state is possible if mechanical defects occur.
Second, the antenna impedance matching in the related art cannot match the antenna impedance optimally for both when the antenna is extracted and when it is retracted.
Third, the antenna impedance matching in the related art only by sensing the casing state cannot match the antenna impedance optimally for both a reception and a transmission mode.